1. Field of the Invention
The present invention relates to a viscous fluid type heat generator in which a viscous fluid is subjected to a shearing stress in a heat generating chamber to generate heat that is in turn transferred to a heat exchanging fluid circulating through a heat receiving chamber to be carried by the heat exchanging fluid to a desired area to be heated. The present invention may be considered to be a supplementary heat source incorporated in a vehicle heating system.
2. Description of the Related Art
In conventional vehicle heating systems, a cooling water or heat exchanging fluid circulating through a fluid circuit for cooling a water-cooled engine is introduced into a heater core or heat exchanger, an air heated through the heater core is discharged into a passenger compartment of the vehicle to thereby heat the latter. In this respect, a vehicle provided with an engine such as a diesel engine or a lean burn engine, which generally provide a relatively low heating value and thus insufficiently heat the heat exchanging fluid, are unlikely to maintain the temperature of the heat exchanging fluid, to be introduced into the heater core at a desired temperature sufficient to heat the passenger compartment, for example, at 80.degree. C. or more. Consequently, the heating systems incorporated in such vehicles are generally liable to lack heating performance for the passenger compartment.
To overcome the above problem, a viscous fluid type heat generator has been provided to be incorporated as a supplementary heat source, in a fluid circuit, through which a cooling water or heat exchanging fluid circulates for cooling the engine. In the known viscous fluid type heat generator, a housing assembly defines therein a heat generating chamber and a heat receiving chamber arranged adjacent to the heat generating chamber. The heat exchanging fluid circulates to be introduced into the heat receiving chamber and to be delivered therefrom to the fluid circuit.
A drive shaft is supported for rotation by a bearing in the housing assembly, and a rotor element is fixedly mounted on the drive shaft to be rotatable within the heat generating chamber. The rotor element includes outer surfaces arranged face-to-face with the inner wall surfaces of the heat generating chamber to define therebetween a small gap. The viscous fluid, such as silicone oil, is supplied into the heat generating chamber in a fluid-tight manner to fill the small gap.
In the vehicle provided with the above viscous fluid type heat generator incorporated into the fluid circuit, when the output torque of the vehicle engine is transferred to the drive shaft of the heat generator to rotationally drive the drive shaft, the rotor element is also rotated within the heat generating chamber. The rotating rotor element provides a shearing stress to the viscous fluid held in the small gap between the inner wall surfaces of the heat generating chamber and the outer surfaces of the rotor element, whereby the viscous fluid generates heat. The generated heat is then transferred from the viscous fluid to the heat exchanging fluid circulating through the heat receiving chamber, and the heat exchanging fluid carries the transferred heat to the fluid circuit of the vehicle heating system to heat the passenger compartment.
In the above-mentioned conventional viscous fluid type heat generator incorporated into the fluid circuit of the cooling water or heat exchanging fluid for cooling the engine, the temperature of the viscous fluid in the heat generating chamber rises when the rotation speed of the engine is increased, regardless of the temperature of the heat exchanging fluid circulating through the fluid circuit. Consequently, when the engine operates at such a high speed that the temperature of the viscous fluid in the heat generating chamber rises and exceeds a limit temperature defining the heat resistant properties of the viscous fluid, the quality of the viscous fluid is apt to be thermally and mechanically deteriorated.
For example, when a silicone oil with high viscosity is used as the viscous fluid, the quality of the silicone oil will be thermally and mechanically deteriorated when the temperature thereof exceeds about 250.degree. C. The deterioration of the viscous fluid reduces the efficiency of heat generation due to the shearing stress applied thereto, which results in the reduction of a heating performance, accomplished by the conventional viscous fluid type heat generator, required to comfortably heat, e.g., the vehicle passenger compartment.